1. Field of Invention
The present invention relates to an installation capable of increasing the usable range of a light source. More particularly, the present invention relates to an installation capable of increasing the usable range along the axial direction of a light source.
2. Description of Related Art
The operating principles of most image-extraction instruments, such as scanners and digital cameras, are very similar. Common features of image-extraction instruments include the use of a light source to produce an optical image and the passing of an optical image through an optical transmission system to an optical sensor. In general, the optical sensor is a charge couple device (CCD).
However, the longitudinal light source of a scanner has one major drawback, namely, brightness level along the central portion of the light axis is usually higher than along the adjacent sides. Hence, an image produced by the light source is brighter in the middle while dimmer along the edges. Since a scanner depends on brightness contrast to operate, a conventional scanner has poorer contrast near the two edges of the light axis. To preserve quality of the scan image, a section near the edge regions is often unused.
Hence, reducing brightness level variation along the axial direction of a light source has become one of the major improvement targets. For example, in Taiwan patent publication no. 244013 entitled ‘Improved lamp shade compensation of an optical scanner’, brightness variation along the light axis is improved by modifying the lamp shade structure. However, the invention requires specially made components, and hence may lead to an increase in production cost.
In Taiwan patent publication no. 352886 entitled ‘A lens structure and its integration with an image-reading device’, another method of improving brightness level along the axial direction of a light source is proposed. By changing the degree of reflectivity of a coated film on the reflecting lens inside the scanner, brightness level variation is reduced. However, the reflectivity of more than one reflecting lens needs to be modified, thereby increasing the production cost necessary for achieving the results. In addition, the method is not suitable for other optical sensing devices besides a scanner.